Knowledge Feature – Dislocations

Pic: Anterior shoulder dislocation (the shoulder popped out and moved forward), similar to the one my husband suffered. Pic courtesy of Wikipedia

My husband was jogging to work this morning, as he usually does in the winter. This morning was different though, because he slipped on some ice and dislocated his shoulder. Luckily his lab is in the hospital anyway, so he just carried on to where he was going, only now with the added stop in the ER to have his shoulder popped back into place. I like to think of myself as being a caring wife, and recognizing that there was no doubt a bit of stress in dealing with doctors and his injury, I didn’t want to bombard him with too many questions and phone calls/texts. But I can’t help that I’m also an osteoarchaeologist with a deep-seeded love for palaeopathology, so my curiosity was killing me. So I asked only three questions: 1) Are you ok? 2) Did it look gross? 3) Can you get me pictures of the xray? 1) Yes, he’s ok (in the grand scheme of things a disclocated shoulder isn’t that bad, and his was only partially dislocated – subluxated). 2) It looked like his shoulder was hunched over so it didn’t look that gross, but it felt gross. 3) I’m still waiting to find out if he was able to get PDF copies of his xrays for me (#truelove).

So I decided that in honour of him, I’m going to spend some of my free time writing an entry on dislocations. They’re not an uncommon injury in today’s populations, but can we see evidence for dislocations in past populations? The answer is yes, we can! Dislocations can make for a risky, gross Google search, so let me save you from going down that dark path by summarizing everything you need to know here.

What is a dislocation?

Anterior dislocation of the tibia from tarsals of the foot, with associated fibula fracture (Wikipedia)

A joint dislocation, AKA luxation, occurs any time there’s an abnormal separation of the bones within a joint. A partial dislocation, or subluxation, is exactly that – a partial separation of the bones within a joint. Our body is full of a huge variety of joints, so in theory dislocations can happen anywhere, from our fingers and toes to our shoulders and hips to our ribs and our spine. For the most part, dislocations are relatively harmless and easy for a doctor to fix mostly by forcefully manipulating the bone back into place, although occasionally surgery is needed. They hurt and there can be associated ligament/tendon/muscle damage, but very few will cause serious damage. And when I say serious damage, I mean serious damage. Spinal dislocations can kill you. Fortunately, they’re not that common. The most common dislocation is a shoulder dislocation, and it’s easy to see why. The socket on the scapula that the humeral head sits in, called the glenoid fossa, is super shallow. Your shoulder is kept in place by a

The shoulder socket and all the ligaments keeping it together (Wikipedia)

whole bunch of ligaments between the humerous (your upper arm), scapula (your shoulder blade), and clavicle (your collar bone). The pro of this is that we have a huge range of motion in our shoulders. The con is that it’s relatively easy to pop out of place. And by “easy” I mean it still takes a lot of force, usually in the form of trauma (i.e. falling). It just doesn’t require as much force as dislocating your femur (your thigh bone) from your innominate (aka coxa, your hip bone), which is a much deeper socket to pop out of.

How do we see dislocations archaeologically?

Looking at archaeological skeletal collections, we can find evidence for dislocations in a few different ways. Firstly, it’s important to note that we can only see evidence of dislocation if it was traumatic enough or occurred frequently enough to affect the bones, or if it was left untreated.

Trauma

Shoulder dislocations, despite being the most common dislocation, haven’t been often

The arrow is pointing to an indent in the bone, that’s a Hills-Sachs lesion (Wikipedia)

reported in archaeological collections. Why is this? Because the shoulder joint (where the humerus connects to the scapula) is so shallow, it’s usually only soft tissue that’s affected. That being said, sometimes we can still see skeletal markers, such as evidence for fractures in the surrounding bones. While researching the coracoid (a little hook of bone on the scapula, which you can see in that illustration above of the shoulder socket) for a conference presentation last year, I discovered that the coracoid fractures are extremely rare, but often occur in association with shoulder dislocations when the head of the humerus hits the coracoid on its way out of its socket. In anterior dislocations if the dislocation is forceful enough, the coracoid could fracture the humeral head instead, causing a little depression in the head called a Hills-Sachs fracture. Alternatively, the humerus could fracture the glenoid fossa, resulting in what’s called a bony Bankart lesion. If these injuries occurred close enough to death, we could see them in archaeological remains, either through a relatively fresh fracture or healing at a fracture site.

Frequent Occurrence

Mitchell and Redfern (2008)’s summary of changes in the skeletal system from DDH

Because the hip socket, called the acetabulum, is so deep it usually requires an enormous amount of force to traumatically dislocate the femur. Due to this, traumatic hip dislocations are rare. Congenital hip dislocations, referred to now as developmental dysplasia/dislocation of the hip, however, are more common than traumatic dislocations and the most frequent type of dislocation reported in archaeology due to the changes seen in the bones of the legs and hips. DDH is actually fairly rare, occurring in only one or two individuals per one thousand (Mitchell and Redfern, 2008). DDH can take 2 forms. Dysplasia, or partial dislocation, is when the head of the femur slides up and down in the acetabulum, causing the acetabulum to take a more oval shape and generally leading to early osteoarthritis. Full dislocation occurs when the head of the femur completely moves out of the acetabulum and creates a pseudoacetabulum to reattach itself to (Blondiaux and Millot, 1991; Mafart et al., 2006; Mitchell and Redfern, 2008, 2011). This results in a characteristic waddling gait. Did you know that the French family names Boite and Boiteux are directly linked to the waddlng gait caused by DDH, using part of the French verb boiter, which means “to lame” (Mafart et al. 2006)? Between the 11th and 13th centuries, French kings issued rules declaring that family names were required for registering births, marriages, and deaths with the church. Those with waddling ancestors ended up stuck with Boite or Boituex as a result.

Anyway, back to the actual skeleton. Being a chronic condition, DDH permanently alters your hip, as I mentioned above. But it also affects more than just the hip. Mitchell and Redfern (2008) put together a lovely summary of how DDH can affect your hips, legs, and spine, causing changes in the shapes and angles these bones would normally have. While DDH is visually obvious, there are times when we may not have the innominates, or they could be too degraded. So knowing how else chronic hip dislocations may affect the skeleton is a super useful set of knowledge to have!

Pic:(there are pop-up captions, but I’ll summarize here) From Mafart et al. (2007) – you can see the large pseudoacetabulum in the picture on the left, on the iliac blade of the hip bone. The cavity below it is the true acetabulum, where the femoral head is supposed to sit. In the pic on the right you can see the associated changes in the femoral head as a result of its dislocation.

Left Untreated

Finally, we come to the most obvious of evidence for dislocation in archaeological remains – when the dislocations were left untreated. As I’ve described above in my discussion on DDH, chronic dislocations can seriously alter the shape of our bones. Leaving a dislocation untreated will (obviously) have the same affects. We’ll see serious changes to the joint sockets and attachment sites, generally through the formation of pseudosockets, like the fake acetabulum, or pseudofacets. Sometimes dislocations were left untreated simply because they weren’t noticed (maybe another related injury, like a fracture, overshadowed the dislocation). Other times they were left untreated simply due to a lack of knowledge of how to fix the dislocation.

Summary/TL;DR

Dislocations are a common injury to have, and yes, we can see evidence of them in the past.

Blondiaux, J. and F. Millot. 1991. Dislocation of the Hip: Discussion of Eleven Cases from Mediaeval France. International Journal of Osteoarchaeology. 1: 203-207.

Dreier, F.G. 1992. The Palaeopathology of a Finger Dislocation. International Journal of Osteoarchaeology. 2: 31-35.

Keenleyside, A. 2003. An Unreduced Dislocated Mandible in an Alaskan Eskimo: A Case of Altruism or Adaptation? International Journal of Osteoarchaeology. 13: 384-389.

Mafart, B., R. Kefi, and E. Beraud-Colomb. 2007. Palaeopathological and Palaeogenetic Study of 13 Cases of Developmental Dysplasia of the Hip with Dislocation in a Historical Population from Southern France. International Journal of Osteoarchaeology. 17: 26-38.

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